In addition to the increased risk of pneumonia accompanying chronic lung diseases, comorbid conditions involving other organ systems also increase pneumonia risk. Despite the substantial differences in each condition, diabetes mellitus, chronic liver disease, kidney disease, and heart failure all show strong increases (e.g., 1.5- to 4-fold) in pneumonia risks (216, 493). The hyperglycemia of diabetes impairs neutrophil chemotaxis (100) and superoxide-mediated antimicrobial effects (383), although clinical trials of strict control of hyperglycemia fail to demonstrate reductions in pneumonia (6, 486b), implying additional mechanisms contributing to susceptibility. Impaired neutrophil function during liver disease (40) is in part related to tuftsin deficiency (499). Tuftsin modulates activities of phagocytic cells, but requires activation in the spleen; splenic congestion from cirrhotic liver disease is hypothesized to impair tuftsin activation. Uremia during chronic kidney disease impairs neutrophil intracellular killing through unclear mechanisms; however, dialysis partially restores neutrophil function (17). Mechanisms of increased pneumonia risk associated with heart failure have not been experimentally elucidated, although some hypothesize that chronic pulmonary edema may generally impair neutrophil and monocyte chemotaxis and function. Importantly, chronic diseases cluster together (e.g., diabetes is a risk factor for liver and kidney disease as well as heart failure). With the exception of targeted vaccination against influenza and pneumococcus, methods to reduce pneumonia risks among patients with chronic disease are unclear and warrant further study. Understanding the pathophysiological interactions between multiple chronic diseases that lead to pneumonia may identify novel opportunities to interrupt etiological pathways.